The present invention relates to a liquid crystal microlens used as a means for forming an image in a lens array for a contact-type sensor for a scanner and facsimile machine.
There is commonly known a contact-type sensor having a construction such as that of FIGS. 14 and 15.
Referring to FIG. 14, a sensor 110 has a frame 108 in which are mounted a linear light-emitting element (LED) array 105, a rod lens array 106, and light-receiving element array 104. The light-receiving element array 104 comprises a substrate 103 formed at the bottom of the frame 108, a protection film 102 mounted on the substrate 103, and a sensor IC 101 comprising a plurality of photoelectric converters. A transparent plate 107 on which a text sheet 109 is set is mounted on the upper portion of the frame 108.
In operation, a light beam from the LED array 105 irradiates the text sheet 109. The light beams diffused and reflected at a particular reading line of the sheet 109 passes through the rod lens array 106 so as to form an image on the text upon the sensor IC of the light-receiving element array 104. Information regarding the shades of the text sheet conveyed by the reflected light, taking the form of the intensity of light, is converted into an electric signal by the sensor IC 101 and serially outputted in accordance with the scanning direction. After scanning one line in the scanning direction, the next line in the direction perpendicular to the scanning direction is scanned. By repeating the scanning operation, two-dimensional information on the text sheet 109 is converted into an electric signal in time sequence. FIG. 15 shows the arrangement of the rod lens array 106 of the contact-type sensor 110 shown in FIG. 14 and the operation thereof.
The principle and the construction of the rod lens array 1106 are described hereinafter with reference to FIGS. 16a to 16c. Each rod lens of the rod lens array 106 is a graded index lens, each having a refractive index distribution shown in FIG. 16a. FIG. 16b shows the transmission of a light beam through the rod lens.
In FIG. 16a, the distribution of the refractive index n can be approximately expressed as
n=n0(1xe2x88x92(A/2)r2) xe2x80x83xe2x80x83(1) 
where n0 is the refractive index on the optical axis, r is the distance from the optical axis in a radial direction, and A is the constant of the refractive index. The light beams tend to travel slower in a range where the refractive index is large and faster where the refractive index is small.
Referring to FIG. 16b, in a graded index rod lens having the refractive index distribution of the equation (1) and a length Z, condition (r2, rxe2x80x22) of an exiting light beam, condition (r1, rxe2x80x21) of the incident light beam can be expressed as follows.                               [                                                    r2                                                                                                          r                    xe2x80x2                                    ⁢                  2                                                              ]                =                              [                                                                                                                              cos                        ⁢                                                  A                                                ⁢                        Z                                            )                                        +                                          (                                              sin                        ⁢                                                  A                                                ⁢                                                  Z                          /                                                      n                            0                                                                          ⁢                                                  A                                                                    )                                                                                                                                                                                      -                                                  n                          0                                                                    ⁢                                              A                                            ⁢                                              xe2x80x83                                            ⁢                                              sin                        ⁡                                                  (                                                                                    A                                                        ⁢                            Z                                                    )                                                                                      +                                          cos                      ⁡                                              (                                                                              A                                                    ⁢                          Z                                                )                                                                                                                  ]                    ⁡                      [                                                            r1                                                                                                                        r                      xe2x80x2                                        ⁢                    1                                                                        ]                                              (        2        )            
The equation (2) means that despite of the difference of the incident position and the incident angle, each light source has the same winding interval (P=2xcfx80/{square root over (A)}), and as shown in FIG. 16c, by setting an appropriate rod lens length Z0 in relation to the winding interval, an erecting image Qxe2x80x3 of an image Q equal in size thereto can be formed at the opposite side of the rod lens at a distance TC.
The reference L0 in FIG. 16c is a working distance between the rod lens and the object Q (Qxe2x80x3).
Thus, even if the end faces are flat, due to the distribution of the refractive index, the rod lens has a lens effect. Namely, the rod lens is provided with the following characteristics.
(1) An erecting image, the size of which is equal to that of the original object, is formed.
(2) The condition of the formed image can be changed dependent on the length of the rod lens, so that the width of the image can be rendered much larger than the diameter of the lens.
Therefore, as shown in FIG. 15, when a plurality of rod lenses are arranged adjacent the other, equal-sized erecting images formed by the rod lenses are overlapped, so that an image on the text sheet can be formed on the light-receiving array 104 without a gap.
Methods for imparting the refractive index distribution to a glass rod include ion implantation, molecular stuffing, and ion exchange method. In the case of rod lens, the ion exchange method is used so that the distribution becomes smooth and symmetrical.
Referring to FIG. 17, the ion exchange method employs a kiln 112 containing a fused salt 113 of high temperature. A glass rod 116 is immersed in the salt 113 so that an alkali ion A in the glass rod and an alkali ion B in the salt 113 are exchanged with each other. As a result, there is formed in the glass rod 116 an ion concentration distribution which is in proportion to the refractive index distribution described above.
However, the rod lens thus formed has the following problems.
(1) In order to manufacture the rod lens, there is a need to provide a device for the ion conversion treatment so that the manufacturing cost increases.
(2) The conjugation length TC, which is the distance between the original object and the image formed, can only be selected from the lineup of the rod lens products. Thus the distance TC cannot be shortened for manufacturing a thin contact-type sensor.
An object of the present invention is to provide a lens means for a contact-type sensor where the above problems are resolved so that inexpensive and thin contact-type sensor can be manufactured.
According to the present invention, there is provided a compound liquid crystal lens comprising a first liquid crystal lens for forming an inverted image of an object, a second liquid crystal lens for inverting the inverted image, thereby forming an erecting image of the object, a supporting member for supporting the first and second liquid crystal lenses in axial symmetry.
Each of the first and second liquid crystal lenses comprises a pair of spaced transparent substrates, a pair of electrodes disposed between the substrates, a liquid crystal material charged in a space between the electrodes, at least one electrode having circular holes, opposite circular holes of the first and second liquid crystal lenses being concentrically disposed.
The supporting member is a transparent glass plate.
In an aspect of the invention, each of the first and second liquid crystal lenses comprises a transparent substrate, a pair of electrodes disposed in a space between the substrate and the glass plate, a liquid crystal material charged in a space between the electrodes, both of the electrodes having opposite concentric circular holes, opposite circular holes of the first and second liquid crystal lenses being concentrically disposed.
These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.